In a photoelectric experiment, the frequency of light is kept fixed above threshold while its intensity is doubled. What happens to the saturation current and the stopping potential?

Saturation current doubles; stopping potential is unchanged

Both saturation current and stopping potential double

Both saturation current and stopping potential are unchanged

Saturation current is unchanged; stopping potential doubles

Light below a metal's threshold frequency falls on it, and its intensity is increased many times. What happens to photoelectric emission?

No emission occurs at any intensity

Emission begins after a long delay

Emission occurs with zero kinetic energy

Emission begins once the intensity is high enough

Dual Nature of Radiation & Matter

31 NEET-UG practice questions on Dual Nature of Radiation & Matter, part of Physics. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A deuteron and an α-particle, both initially at rest, are accelerated through the same potential difference. What is the ratio of the de Broglie wavelength of the deuteron to that of the α-particle?
1. A4
2. B2
3. C1/2
4. D√2
Show answerHide answer
Answer: B · 2
λ = h/√(2mqV), so at the same V, λ is proportional to 1/√(mq). Deuteron: mq = 2 × 1 = 2. α-particle: mq = 4 × 2 = 8. The ratio is √(8/2) = 2.
- A: The square root was not taken.
- C: The ratio has been inverted.
- D: The factor from the charge was left out, using 1/√m only.
Remember this
Through the same potential, de Broglie wavelength varies as 1/√(mq), so a larger mass and charge both shorten it.
Question 2 · Hard
A metal is lit in turn by light of wavelength 200 nm and of 400 nm. The stopping potential with 200 nm is three times that with 400 nm. Taking hc = 1240 eV nm, find the work function of the metal.
1. A4.65 eV
2. B3.1 eV
3. C7.75 eV
4. D1.55 eV
Show answerHide answer
Answer: D · 1.55 eV
Photon energies are 1240/200 = 6.2 eV and 1240/400 = 3.1 eV. Then 6.2 - φ = 3(3.1 - φ), so 2φ = 3.1 and φ = 1.55 eV. Check: stopping potentials 4.65 V and 1.55 V, ratio 3.
- A: This is the stopping energy with 200 nm light.
- B: This is the photon energy of 400 nm light, not the work function.
- C: The factor of 3 was applied to the wrong wavelength.
Remember this
Write eV₀ = hc/λ - φ for each wavelength and solve the pair; the work function does not change.
Question 3 · Medium
In a photoelectric experiment, the frequency of light is kept fixed above threshold while its intensity is doubled. What happens to the saturation current and the stopping potential?
1. ABoth saturation current and stopping potential double
2. BSaturation current doubles; stopping potential is unchanged
3. CBoth saturation current and stopping potential are unchanged
4. DSaturation current is unchanged; stopping potential doubles
Show answerHide answer
Answer: B · Saturation current doubles; stopping potential is unchanged
Doubling intensity doubles the photons per second, and so the electrons emitted per second and the saturation current. The stopping potential depends on hν - φ, which has not changed.
- A: Stopping potential does not depend on intensity.
- C: More photons per second do raise the saturation current.
- D: This reverses the roles of intensity and frequency.
Remember this
Intensity controls photocurrent; frequency and work function control stopping potential.
Question 4 · Easy
Light below a metal's threshold frequency falls on it, and its intensity is increased many times. What happens to photoelectric emission?
1. AEmission begins after a long delay
2. BNo emission occurs at any intensity
3. CEmission occurs with zero kinetic energy
4. DEmission begins once the intensity is high enough
Show answerHide answer
Answer: B · No emission occurs at any intensity
Each photon has energy hν, and one electron absorbs one photon. Below threshold, hν is less than the work function, so no electron can escape, however many photons arrive.
- A: Emission is instantaneous when it occurs, and here it does not occur at all.
- C: An electron cannot escape without energy at least equal to the work function.
- D: More photons do not help, as one photon gives its energy to one electron.
Remember this
Emission depends on frequency, not intensity; above threshold, intensity sets the number of electrons, frequency their energy.
Question 5 · Easy
Photons of energy 5.0 eV strike a metal of work function 2.0 eV. What stopping potential do the emitted electrons have?
1. A7.0 V
2. B5.0 V
3. C3.0 V
4. D2.5 V
Show answerHide answer
Answer: C · 3.0 V
Einstein's equation gives K_max = hν - φ = 5.0 - 2.0 = 3.0 eV. The stopping potential satisfies eV₀ = K_max, so V₀ = 3.0 V.
- A: The work function was added instead of subtracted.
- B: The work function was ignored.
- D: The photon energy was divided by the work function.
Remember this
eV₀ = hν - φ, so the stopping potential in volts equals the maximum kinetic energy in eV.
Question 6 · Medium
Assertion A: Graphs of stopping potential against frequency for two different metals are parallel straight lines. Reason R: The slope of each graph equals the work function of the metal divided by e. Choose the correct answer.
1. ABoth A and R are correct but R is not the correct explanation of A
2. BA is not correct but R is correct
3. CBoth A and R are correct and R is the correct explanation of A
4. DA is correct but R is not correct
Answer and explanation in LearnFree account
Question 7 · Medium
Stopping potential is plotted against frequency for two metals P and Q. If light of frequency 10 × 10¹⁴ Hz falls on each, what is the ratio of the maximum kinetic energy of photoelectrons from P to that from Q?
Figure: MedExams
1. A3 : 2
2. B1 : 1
3. C5 : 3
4. D2 : 3
Answer and explanation in LearnFree account
Question 8 · Easy
Maximum kinetic energy of photoelectrons from a metal is plotted against the frequency of the incident light. Using h = 6.6 × 10⁻³⁴ J s, what is the work function of the metal?
Figure: MedExams
1. A9.9 × 10⁻¹⁹ J
2. B5.0 × 10⁻¹⁹ J
3. C3.3 × 10⁻¹⁹ J
4. D6.6 × 10⁻¹⁹ J
Answer and explanation in LearnFree account
Question 9 · Medium
A photocell is lit by light of one frequency at two intensities, I₁ > I₂. Which graph correctly shows photocurrent i against anode potential V for both?
Figure: MedExams
1. AGraph A
2. BGraph C
3. CGraph D
4. DGraph B
Answer and explanation in LearnFree account
Question 10 · Hard
A proton (mass m, charge e), a deuteron (mass 2m, charge e) and an alpha particle (mass 4m, charge 2e) are each accelerated from rest through a potential difference V. Lines P, Q and R plot their de Broglie wavelengths against 1/√V. Identify the lines.
Figure: MedExams
1. AP: proton, Q: alpha particle, R: deuteron
2. BP: alpha particle, Q: deuteron, R: proton
3. CP: deuteron, Q: proton, R: alpha particle
4. DP: proton, Q: deuteron, R: alpha particle
Answer and explanation in LearnFree account
Question 11 · Hard
Light of wavelength λ falling on a metal gives a stopping potential of 2V₀. Light of wavelength 1.5λ on the same metal gives a stopping potential of V₀. What is the threshold wavelength of the metal?
1. A4.5λ
2. B2λ
3. C3λ
4. D6λ
Answer and explanation in LearnFree account
Question 12 · Medium
An electron starts from rest and is accelerated through a potential difference of 100 V. What is its de Broglie wavelength, approximately?
1. A12.3 nm
2. B0.0123 nm
3. C0.123 nm
4. D1.23 nm
Answer and explanation in LearnFree account
Question 13 · Medium
A metal surface has a work function of 2.48 eV. What is the longest wavelength of light that can eject photoelectrons from it? Take hc = 1240 eV nm.
1. A500 nm
2. B1000 nm
3. C250 nm
4. D3075 nm
Answer and explanation in LearnFree account
Question 14 · Easy
In the photoelectric effect, emission starts with no noticeable delay even when the incident light is very weak. What does this support?
1. AElectrons slowly collect energy from the light wave
2. BLight energy is delivered in discrete packets, each absorbed by a single electron
3. CThe work function of a metal falls when light is weak
4. DLight energy spreads evenly over the whole surface
Answer and explanation in LearnFree account
Question 15 · Medium
Given below are two statements: Statement I: The maximum kinetic energy of photoelectrons increases linearly with the frequency of the incident light, above the threshold. Statement II: The slope of the graph of stopping potential against frequency is the same for all metals. Choose the correct answer.
1. ABoth Statement I and Statement II are incorrect
2. BBoth Statement I and Statement II are correct
3. CStatement I is correct but Statement II is incorrect
4. DStatement I is incorrect but Statement II is correct
Answer and explanation in LearnFree account
Question 16 · Medium
For each of two different metals, the stopping potential V₀ is measured at several frequencies ν and plotted against ν. How do the two straight lines compare?
1. AThey pass through the origin with slopes set by the work functions
2. BThey are parallel, with slope e/h, and coincide
3. CThey meet at one point on the frequency axis but have different slopes
4. DThey are parallel, with slope h/e, but cut the frequency axis at different points
Answer and explanation in LearnFree account
Question 17 · Hard
A 6.6 mW beam of light of wavelength 600 nm falls on a metal of work function 1.8 eV. On average one photoelectron is emitted for every 100 incident photons, and all of them reach the collector. Taking h = 6.6 × 10⁻³⁴ J s, c = 3 × 10⁸ m/s and e = 1.6 × 10⁻¹⁹ C, what saturation current flows?
1. A32 µA
2. B3.2 mA
3. C0.32 µA
4. D32 mA
Answer and explanation in LearnFree account
Question 18 · Medium
Suppose a proton and an alpha particle are moving with equal kinetic energies. Taking the mass of the alpha particle as four times that of the proton, what is the ratio of the de Broglie wavelength of the proton to that of the alpha particle?
1. A1 : 2
2. B4 : 1
3. C2 : 1
4. D2√2 : 1
Answer and explanation in LearnFree account
Question 19 · Easy
Light falls on a metal surface and ejects photoelectrons. Which change increases the maximum kinetic energy of the emitted electrons?
1. ARaising the intensity of the light
2. BRaising the frequency of the light
3. CKeeping the light on for a longer time
4. DMaking the collector more positive
Answer and explanation in LearnFree account
Question 20 · Medium
Ultraviolet light of wavelength 310 nm falls on a metal of work function 2.5 eV. Taking hc = 1240 eV nm, what stopping potential is needed to cut off the photocurrent?
1. A4 V
2. B2.5 V
3. C1.5 V
4. D6.5 V
Answer and explanation in LearnFree account
Question 21 · Medium
A ball of mass 0.1 kg moving at 6.6 m/s has a de Broglie wavelength of 10⁻³³ m. Why are its wave properties never observed in practice?
1. AIts speed is too low for a matter wave to form
2. BIts wavelength is far smaller than any aperture or obstacle, so no diffraction can be detected
3. CThe ball is uncharged, and only charged particles have matter waves
4. DBodies of macroscopic mass have no de Broglie wave at all
Answer and explanation in LearnFree account
Question 22 · Easy
Taking h = 6.6 × 10⁻³⁴ J s and c = 3 × 10⁸ m/s, what is the momentum of a photon of wavelength 660 nm?
1. A3.3 × 10⁻³⁶ kg m/s
2. B1.0 × 10⁻²⁷ kg m/s
3. C3.0 × 10⁻¹⁹ kg m/s
4. D1.0 × 10⁻²⁴ kg m/s
Answer and explanation in LearnFree account
Question 23 · Medium
An electron and a photon have the same de Broglie wavelength. Which quantity must then be the same for both?
1. AEnergy
2. BMass
3. CMomentum
4. DSpeed
Answer and explanation in LearnFree account
Question 24 · Hard
Photons emitted when hydrogen atoms fall from n = 2 to n = 1 strike a metal of work function 4.2 eV. Taking Eₙ = −13.6/n² eV, and the de Broglie wavelength of an electron of kinetic energy K (in eV) as 1.227/√K nm, what is the de Broglie wavelength of the fastest photoelectrons?
1. A0.32 nm
2. B0.20 nm
3. C0.38 nm
4. D0.50 nm
Answer and explanation in LearnFree account
Question 25 · Easy
Taking hc = 1240 eV nm, what is the energy of a photon of wavelength 620 nm?
1. A3.2 × 10⁻¹⁹ eV
2. B2.0 eV
3. C20 eV
4. D0.5 eV
Answer and explanation in LearnFree account

6 more Dual Nature of Radiation & Matter questions

Answer them one by one, keep your score and see your weak topics in Learn. Signed-out visitors try 25 per exam; sign in with Google to see them all.

Study Physics

Dual Nature of Radiation & Matter

A deuteron and an α-particle, both initially at rest, are accelerated through the same potential difference. What is the ratio of the de Broglie wavelength of the deuteron to that of the α-particle?

A metal is lit in turn by light of wavelength 200 nm and of 400 nm. The stopping potential with 200 nm is three times that with 400 nm. Taking hc = 1240 eV nm, find the work function of the metal.

In a photoelectric experiment, the frequency of light is kept fixed above threshold while its intensity is doubled. What happens to the saturation current and the stopping potential?

Light below a metal's threshold frequency falls on it, and its intensity is increased many times. What happens to photoelectric emission?

Photons of energy 5.0 eV strike a metal of work function 2.0 eV. What stopping potential do the emitted electrons have?

Assertion A: Graphs of stopping potential against frequency for two different metals are parallel straight lines. Reason R: The slope of each graph equals the work function of the metal divided by e. Choose the correct answer.

Stopping potential is plotted against frequency for two metals P and Q. If light of frequency 10 × 10¹⁴ Hz falls on each, what is the ratio of the maximum kinetic energy of photoelectrons from P to that from Q?

Maximum kinetic energy of photoelectrons from a metal is plotted against the frequency of the incident light. Using h = 6.6 × 10⁻³⁴ J s, what is the work function of the metal?

A photocell is lit by light of one frequency at two intensities, I₁ > I₂. Which graph correctly shows photocurrent i against anode potential V for both?

A proton (mass m, charge e), a deuteron (mass 2m, charge e) and an alpha particle (mass 4m, charge 2e) are each accelerated from rest through a potential difference V. Lines P, Q and R plot their de Broglie wavelengths against 1/√V. Identify the lines.

Light of wavelength λ falling on a metal gives a stopping potential of 2V₀. Light of wavelength 1.5λ on the same metal gives a stopping potential of V₀. What is the threshold wavelength of the metal?

An electron starts from rest and is accelerated through a potential difference of 100 V. What is its de Broglie wavelength, approximately?

A metal surface has a work function of 2.48 eV. What is the longest wavelength of light that can eject photoelectrons from it? Take hc = 1240 eV nm.

In the photoelectric effect, emission starts with no noticeable delay even when the incident light is very weak. What does this support?

For each of two different metals, the stopping potential V₀ is measured at several frequencies ν and plotted against ν. How do the two straight lines compare?

Suppose a proton and an alpha particle are moving with equal kinetic energies. Taking the mass of the alpha particle as four times that of the proton, what is the ratio of the de Broglie wavelength of the proton to that of the alpha particle?

Light falls on a metal surface and ejects photoelectrons. Which change increases the maximum kinetic energy of the emitted electrons?

Ultraviolet light of wavelength 310 nm falls on a metal of work function 2.5 eV. Taking hc = 1240 eV nm, what stopping potential is needed to cut off the photocurrent?

A ball of mass 0.1 kg moving at 6.6 m/s has a de Broglie wavelength of 10⁻³³ m. Why are its wave properties never observed in practice?

Taking h = 6.6 × 10⁻³⁴ J s and c = 3 × 10⁸ m/s, what is the momentum of a photon of wavelength 660 nm?

An electron and a photon have the same de Broglie wavelength. Which quantity must then be the same for both?

Photons emitted when hydrogen atoms fall from n = 2 to n = 1 strike a metal of work function 4.2 eV. Taking Eₙ = −13.6/n² eV, and the de Broglie wavelength of an electron of kinetic energy K (in eV) as 1.227/√K nm, what is the de Broglie wavelength of the fastest photoelectrons?

Taking hc = 1240 eV nm, what is the energy of a photon of wavelength 620 nm?